puhlfly
Aquarium Advice Apprentice
I don't know if it will effect sandstone or not, but a good first test for rocks is white vinegar. Rinse the rock then pour some vinegar on it, if it fizzes don't use the rock. This can weed out candidates before doing water test experiments. Be careful with sanstone I think it could be a sourcce of minerals (good and not ) for your water. It could break down over time.